1. Field of the Invention
The present invention relates to electrophotographic image forming apparatuses such as digital multifunction machines that carry out image forming using a two-component developer containing toner and a carrier, and to toner replenishment control methods.
2. Description of the Related Art
Some conventional electrophotographic image forming apparatuses involve charging a surface of an image bearing member (for example, a photosensitive body), then forming an electrostatic latent image on a charged region thereof by performing image exposure (for example, irradiating a laser beam) based on image data that has been stored in a storage portion. This electrostatic latent image is made into a visible image (developed) as a toner image by a development apparatus, and after this toner image that has been made into a visible image is electrostatically transferred to a recording material such as a recording paper, the toner image that has been transferred to the recording material is made to bind to the recording material by a fixing apparatus.
When carrying out developing using a two-component developer containing toner and a carrier in this type of image forming apparatus, a system is generally employed involving causing only the toner to adhere to the image bearing member and be consumed, the toner being from the toner and carrier in the developer that is borne on a developer bearing member in the development apparatus. For this reason, toner replenishment control is implemented by which toner is replenished as appropriate to the developer in order to properly maintain a concentration of toner in the developer in the development apparatus.
In image forming apparatuses that use a two-component developer, ordinarily the concentration of toner in the developer is directly or indirectly detected by a sensor, and control of replenishment of toner to the developer is carried out based on these detection values. A magnetic permeability sensor that detects the carrier component in the developer can be given as a typical example of a sensor that detects the concentration of toner in the developer.
With these conventional image forming apparatuses, it is generally common that toner replenishment control is carried out using only the detection values of the sensor that detects the toner concentration, and in this case there is no implementation of toner replenishment control conforming to the image data that corresponds to the electrostatic latent image on the image bearing member, which is to be developed by the developer.
In this regard, JP H09-160364A discloses an image forming apparatus in which toner replenishment control is carried out without using a sensor that detects the toner concentration by detecting a number of pixels to be written so as to estimate a toner consumption amount.
However, although toner replenishment control can be carried out in the image forming apparatus described in JP H09-160364A based on the toner consumption amount that is estimated from the image data, there are cases where error accumulates since no sensor is used to detect the toner concentration. For this reason, there is a risk that the toner concentration will deviate greatly from the proper value as image forming is carried out, and there will be poor accuracy in estimating the toner consumption amount. Consequently, the accuracy of toner replenishment control will worsen.